The main aims of this proposal are to develop recombinant adeno-associated virus 3 (AAV3) serotype vectors for high-efficiency transduction of hepatocytes, and to evaluate the safety and efficacy of the optimized AAV3 serotype vectors in non-human primates, with the long-term goal of their potential use in liver-directed gene therapy in humans. We have observed that of the 10 most commonly used AAV serotypes, AAV3 vectors transduce human liver cancer cell lines extremely efficiently. AAV3 vectors also transduce primary human hepatocytes efficiently, as they utilize human hepatocyte growth factor receptor (HGFR) as a cellular co-receptor. Based on our recent studies on the development of the next generation of AAV2 vectors containing mutations in the surface-exposed tyrosine residues, which transduce murine hepatocytes exceedingly well at low doses, we have also generated tyrosine-mutant AAV3 serotype vectors, and identified an optimized vector that efficiently transduces human liver tumors in a murine xenograft model in vivo. We now wish to parlay some of this information to explore whether optimized AAV3 vectors are the ideal serotype for high-efficiency transduction of human hepatocytes. We propose to test the following hypotheses: a. High-efficiency transduction of primary human hepatocytes can be achieved by optimized AAV3 serotype vectors in a mouse xenograft model in vivo. b. The safety and efficacy of the systemically delivered optimized AAV3 serotype vectors, prior to their potential use in human gene therapy, can be evaluated in a non-human primate model for liver-directed gene transfer in vivo. The following two Specific Aims will be pursued: Specific Aim 1: Development of optimized surface-exposed tyrosine-, serine and threonine-mutant AAV serotype 3 vectors for high-efficiency transduction of human hepatocytes. Specific Aim 2: Biodistribution and safety of optimized AAV3 serotype vectors in non-human primates following systemic delivery. A better understanding of the AAV3-hepatocyte interactions at the molecular level is likely to lead to development of safe and effective vectors for their potential use in gen therapy of human liver diseases in general, and hemophilia B in particular.